Stephen K. Van Den Eeden, a senior investigator at the Division of Research at Kaiser Permanente Northern California, in Oakland says:
"We already know that there are certain risks of amphetamine use. This is one concern that is unproven, but we need to take into consideration whether the benefits outweigh the known risks, and maybe potential risks."
Amphetamines affect the release and absorption of dopamine, a key neurotransmitter implicated in the development of Parkinson's disease. They are commonly prescribed for the treatment of attention-deficit hyperactivity disorder (ADHD), traumatic brain injuries and a chronic sleep disorder known as narcolepsy. These medications were also being routinely prescribed for weight loss when the research first began.
Dopamine is classified as a catecholamine (a class of molecules that serve as neurotransmitters and hormones). It is a monoamine (a compound containing nitrogen formed from ammonia by replacement of one or more of the hydrogen atoms by hydrocarbon radicals). Dopamine is a precursor (forerunner) of adrenaline and a closely related molecule, noradrenaline. Dopamine is formed by the decarboxylation (removal of a carboxyl group) from dopa.
Parkinson's disease is believed to be related to low levels of dopamine in certain parts of the brain. When dopa is taken by mouth, it crosses through the blood-brain barrier. Once it has crossed from the bloodstream into the brain, it is converted to dopamine. The resulting increase in dopamine concentrations in the brain is thought to improve nerve conduction and to assist in lessening the movement disorders in Parkinson disease.
In 1970 the FDA (Food and Drug Administration) approved dopa in the form of L-Dopa, or levodopa, for use in the US. The drug revolutionized the treatment of Parkinson disease.
Dr. Stacy Horn, an assistant professor of clinical neurology at the University of Pennsylvania's Parkinson's Disease & Movement Disorders Center in Philadelphia, explains:
"Someone who failed all the other classic medicines might consider drugs such as amphetamines. We need to confirm the science. There needs to be some increased surveillance. We should look at patients that have had an addiction, and see if there's an increased risk in those populations. Part of the problem is not knowing if this is a direct correlate or exposure to something else."
Horn also emphasized that researchers still don't understand what factors might explain the development of Parkinson's disease, although previous research has hinted at a link to exposure to environmental toxins.
Parkinson's disease (PD) belongs to a group of conditions called motor system disorders, which are the result of the loss of dopamine-producing brain cells. The four primary symptoms of PD are tremor, or trembling in hands, arms, legs, jaw, and face; rigidity, or stiffness of the limbs and trunk; bradykinesia, or slowness of movement; and postural instability, or impaired balance and coordination.
As these symptoms become more pronounced, patients may have difficulty walking, talking, or completing other simple tasks. PD usually affects people over the age of 50. Early symptoms of PD are subtle and occur gradually. In some people the disease progresses more quickly than in others. As the disease progresses, the shaking, or tremor, which affects the majority of PD patients may begin to interfere with daily activities.
Other symptoms may include depression and other emotional changes; difficulty in swallowing, chewing, and speaking; urinary problems or constipation; skin problems; and sleep disruptions. There are currently no blood or laboratory tests that have been proven to help in diagnosing sporadic PD. Therefore the diagnosis is based on medical history and a neurological examination. The disease is extremely difficult to diagnose accurately.
Source: National Institute of Neurological Disorders and Stroke